In piston type pump apparatus, it is desirable to ensure that no gaseous material is allowed to enter the cylinder and develop a cushion or volume of material which is subject to reexpansion and which interferes with the ability of the pump piston to displace a desired volume of gas during each stroke of the piston. For example, U.S. Pat. No. 2,396,602 of Posch describes the problem of gas interference in liquid pumps. Piston energized pump design for liquids is not typically concerned with problems of unswept or unpurged volume within the cylinder, simply because the liquid material remains substantially incompressible during virtually all phases of liquid pressurization that occurs.
In the case of fluid transfer apparatus that is adapted to transfer gaseous material, such as gas compressors, gas evacuation apparatus, for example, the presence of unswept volumes within a cylinder directly affects the volumetric efficiency of the gas transfer apparatus. During the compression stroke of piston energized gas transfer apparatus, with the piston at top dead center, there typically remains a small unswept or unpurged volume of compressed gas that does not escape through the exhaust valve of the pump. As the piston then begins its intake stroke, the typical pressure energized intake valve is caused to remain closed by the pressurized gas in this unswept volume and the gas merely reexpands during an initial portion of the intake stroke of the piston. After the pressure of the reexpanding unswept volume of gas is depleted, further movement of the piston during the intake stroke will develop a negative pressure within the enlarging cylinder chamber between the piston and valve and this negative pressure will develop a pressure differential across the intake valve, overcoming the usual spring bias of the intake valve and causing it to open. Further movement of the piston during intake stroke will then cause gas to be drawn through the intake valve, thus charging the cylinder with a fresh, uncompressed supply of gaseous material which is then compressed as the piston reverses its direction of movement at bottom dead center and then begins a compression stroke toward top dead center.
Where residual compressed gas remains within the cylinder at the end of a compression stroke, the compressed gas will be rather hot. Subsequent inlet of ambient gas into the cylinder during an intake stroke causes mixing of cool ambient gas with the hot previously compressed gas. The result of such mixing is an increase in the temperature of the ambient gas, thus detracting from the volumetric efficiency of the gas pumping operation. It is desirable to pump ambient gas as cool as possible so as to enhance volumetric efficiency and to avoid mixing of hot gas with cool ambient gas prior to compression thereof.
The net effect of the unswept volume within typical gas compressors, vacuum pumps and the like is continual recompression and reexpansion of the small unswept volume, which exists as a limiting factor on volumetric efficiency. Obviously, the piston energized pump mechanism would be efficient from a volumetric standpoint if the unswept or unpurged volume within the cylinder could be eliminated upon each compression stroke of the cylinder. If this should occur, then no gas reexpansion would occur during an intake stroke and the cylinder would be substantially 100% charged during each intake stroke and substantially 100% discharged at the end of each compression stroke.
From a theoretical standpoint, it may be possible to design a piston energized pump mechanism having cylinder purging that approaches 100%. For example, U.S. Pat. No. 1,137,751 of Gaede discusses the provision of a vacuum pump mechanism wherein a piston that reciprocates within a cylinder is caused to contact an immovable internal wall defined at one extremity of the cylinder. It is well understood that a pump mechanism such as that shown in the patent to Gaede is not commercially feasible since mechanical damage and deterioration would occur each time the moving piston element contacts the immovable end wall of the cylinder. The requirement for manufacturing tolerances would therefore dictate that the end wall of the piston be in spaced relation with the immovable cylinder wall at top dead center, therefore defining a small unpurged volume within the cylinder at top dead center. This unpurged volume, of course, detracts from the volumetric efficiency of the compressor mechanism and the volumetric efficiency of the compressor, therefore, falls off considerably as the maximum pressure of the unit increases.
Other compressor systems have been developed for the purpose of achieving substantially complete purge of gas at each compression stroke of the piston. For example, U.S. Pat. Nos. 600,841 of Oderman; 1,488,683 of Juruick; 947,536 of Wenkel; and 2,327,269 Jessup each teach the provision of discharge valve elements that seal about the entire periphery of the cylinder. Further, the Oderman and Jessup patents teach the provision of an inlet valve of the poppet valve type which is incorporated within the discharge valve. The patent of Wendel teaches the use of a reed type inlet valve which is also incorporated within a reed or flexible plate type discharge valve. Although these valves, from a theoretical standpoint, are capable of achieving complete purging of the cylinder at each compressive stroke of the piston, in order to accomplish sealing of the discharge valve with respect to a sealing surface formed about the cylinder, it is necessary that the cylinder bore and discharge valve seat be precisely oriented with respect to one another. Precision machining of this nature is extremely difficult to accomplish and therefore results in extremely high manufacturing costs. Further, it is also necessary that the discharge valve and the bore within which the discharge valve reciprocates, be accurately machined and precisely aligned with respect to the bore of the cylinder and the discharge valve sealing surface at the end wall of the cylinder. Again, such machining operations are extremely difficult and expensive to accomplish and thereby detract from the commercial feasibility of compressor systems of this nature.
Under circumstances where discharge valve sealing is accomplished about the entire periphery of the cylinder, it is, of course, required that the discharge valve be of larger diameter than the cylinder. The discharge valve is, therefore, of quite large and heavy construction, especially where the compressor system is adapted for high pressure pumping operations, and therefore, the discharge valve mechanism has sufficiently high inertia as to detract materially from the operational capability thereof. For efficient high speed pumping operations, it is desirable that the discharge valve have low inertia characteristics in order that it be enabled to move rapidly and efficiently responsive to appropriate pressure conditions within the cylinder and discharge chambers.
In many cases where high pressure compressor operation is required and where large volumes of compressed gas may be required intermittently, it is difficult and expensive to provide compressor power systems having the capability of initiating compressor operation under high pressure load. For this example, it is desirable in many cases to provide a feature typically referred to as suction unloading, which allows the power system to start or remain operating under little or no load. After the power system has been energized and reaches operational capability, the suction unloading system is inactivated, thereby allowing the operating power system to become loaded while operating normally. This feature allows the design of the power system to be of smaller magnitude and therefore typically of less expensive nature and generally prevents premature deterioration of the compressor power system. When a compressor is operating and the receiver tank reaches its maximum desired pressure, it is common to diminish or cease the compressor's pumping ability while maintaining its operational RPM. This is accomplished by the suction unloading process and the resulting energy consumed is lessened considerably with a totally unloading compressor requiring only the energy necessary for its mechanical friction. As the compressor unit increases in size, the more economically favorable it becomes to allow it to remain at operational RPM without pumping rather than to restart it from rest, as required. In the case of compressor systems incorporating discharge valves that seal about the entire periphery of the cylinder and especially under circumstances where the discharge valve and inlet valves are incorporated in a single mechanical unit, it is extremely difficult to accomplish suction unloading. It is therefore desirable to provide a compressor system having the capability of accomplishing substantially 100% purging of the compressor cylinder at each compression stroke and yet achieve suction unloading under circumstances where such is desirable.
In view of the foregoing, it is a primary feature of the present invention to provide a novel gas pump system for positive pressure and vacuum application which has the capability of accomplishing 100% purge of the cylinder at each compression stroke thereof and thereby avoids gas reexpansion within the cylinder which otherwise would interfere with the volumetric efficiency thereof.
It is also a feature of this invention to provide a novel gas pumping mechanism wherein virtually no residual compressed heated gas is allowed to remain in the pump cylinder at the end of a compression stroke and thus mixing of heated gas with cool ambient gas does not occur.
It is another feature of this invention to provide a novel gas pumping mechanism wherein the discharge valve provides an unrestricted opening that minimizes resistance to discharge and therefore also minimizes the pressure induced force acting on the piston.
It is another feature of this invention to provide a novel compressor mechanism incorporating a compressor head structure that accommodates angular and lateral misalignment of parts and promotes efficient sealing of the discharge valve regardless of such lateral and angular misalignment.
It is an even further feature of this invention to provide a novel gas compressor mechanism incorporating a discharge valve construction of low inertia characteristics which will function efficiently under high speed compressor operation.
Among the several features of this invention is noted the provision of a novel gas compressor construction which incorporates a floating discharge and inlet valve assembly that defines a plane at the end of the cylinder when seated thereon and wherein the end wall of the piston of the compressor mechanism is adapted to move beyond this plane to a top dead center position.
It is an even further feature of this invention to provide a novel compressor mechanism incorporating a discharge valve that is lifted from its seated relationship by means of a cushion of compressed gas driven by the piston of the compressor and wherein the discharge valve achieves 360.degree. exhaust of compressed gas into the discharge chamber of the compressor mechanism.
It is an even further feature of this invention to provide a novel compressor mechanism wherein seating of the discharge valve about one end of the cylinder of the compressor is achieved by the force of mechanical urging means and wherein discharge valve positioning and control is assisted by means of a pressure balanced control device.
Another feature of this invention concerns a gas pumping mechanism incorporating a discharge valve and control device that is capable of functioning in any one of several conditions including pneumatically unbalanced, mechanically induced and pneumatically induced.
It is also a feature of this invention to provide a novel gas compressor mechanism incorporating a discharge valve control spool assembly which is sealed with respect to a compressor head structure by O-ring type seals that have rolling rather than sliding characteristics to enhance the functional sealing life thereof.
It is another feature of this invention to provide a novel gas pumping mechanism incorporating a discharge valve control spool assembly which may be sealed with respect to a pump head by suitable sealing means including metal diaphragms, sliding seal elements and the like.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon consideration of this entire disclosure. The form of the invention, which will now be described in detail, illustrates the general principles of the invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention.